This invention relates, in general, to cathode ray tube display devices for producing images of enhanced contrast and, in particular, to a novel screen structure for achieving such contrast.
The contrast of an image reproduced upon the screen of cathode ray tube is adversely affected by ambient light incident upon the viewing surface of the tube's face plate. This obtains because that portion of the ambient light reflected back from the screen tends to desaturate the reproduced image. On the other hand, contrast is enhanced if reflectance, which can be considered a ratio of the quantity of reflected light, to total incident light, is kept minimal. Accordingly, in any image reproducing device for use in home entertainment apparatus, such as television receivers, as well as those devices employed in computer display terminals, it is important that the display presented to the viewer (terminal operator) exhibit minimal reflectance while still maintaining acceptable brightness and resolution.
In addition to attractive reflectance and brightness characteristics a consideration of particular concern, as respects display monitors used in conjunction with computer terminals, is the hue or coloration of the displayed image. In this regard, and in certain situations, it has been determined that a computer terminal operator experiences less eye fatigue when viewing an amber tinted display than when looking at the conventional greenish color exhibited by the excited phosphor of a conventional computer display device.
One solution to the problem is to epoxy bond a filter, in the form of an amber tinted sheet of plastic material, to the faceplate of the display device. While this does provide an amber tinted image, the application of the filter is not without problems. First, the amber tinted material is not inexpensive. Secondly, epoxy bonding the filter to the faceplate is a disagreeable chore, to say the least, which is followed, in turn, by the equally onerous task of removing excess epoxy from the perimeter of the faceplate, as well as from the funnel portion of the tube. Finally, a particularly objectionable problem with this filter arrangement is that, in use, the plastic sheet easily succumbs to scratches.
In the field of tri-color image display devices for television receivers, there has been and continues to be, extensive activity toward the development of screens which have attractive reflectance and brightness properties but, which do not overly cost burden the manufacturing process. An early advance in this art is the subject of U.S. Pat. No. 3,146,368 which issued on Aug. 25, 1964 to Joseph P. Fiore et al. This patent discloses a screen structure, now popularly referred to as a black-surround screen, which is characterized by the placement of light absorbing pigments between each of the phosphor deposits that form the screen structure. The implementation of the teaching of this patent permitted the brightness of mass produced tri-color picture tubes to be effectively doubled.
Another teaching, addressed to the improvement of the contrast and brightness aspects of the screen, is disclosed in U.S. Pat. No. 3,114,065, which issued on Dec. 10, 1963 to Sam H. Kaplan. Kaplan describes combining each of the three basic phosphor materials making up the tri-color screen with a filter that is highly transmissive of the color, or wavelength of light emitted by its associated phosphor material, but which otherwise is an attenuator throughout the visible spectrum. This filter was interposed, as a layer, between the phosphor and the inside surface of the face plate or, alternatively, the filter material could be mixed with the phosphor and the mixture applied to the elemental screen areas.
Another approach to achieve the advantages of black-surround, though structurally quite different, is disclosed in U.S. Pat. No. 3,569,761 which issued on Mar. 9, 1971 to Howard G. Lange. In this patent each elemental area of the screen, assigned to a particular color, is provided with a phosphor deposit and a filter. The phosphor emits light of the color appropriate to its assigned area while the filter is colormetrically related to be highly transmissive of that color but otherwise to serve as an attenuator for visible light. In addition, the filter elements extend over or bridge the spaces between the elemental areas of the screen so that these spaces receive at least two overlapping filter elements. Because of the characteristics of the various filters, the spaces intervening the elemental areas of the screen assigned to specific colors are provided with light attenuators and thus serve, essentially, the same function as the black-surround material described in the Fiore et al patent. While the Lange screen did achieve a black-surround type advantage without the re-etch requirement of Fiore et al, it did so at some sacrifice of screen brightness due, principally, to shortcomings inherent in the optical filter art.
Thereafter, and still in the pursuit of a tri-color tube having attractive reflectance and brightness properties, came the teaching in U.S. Pat. No. 3,812,394 which issued to Sam H. Kaplan on May 21, 1974. Basically, Kaplan here teaches the use of a red filter formed of a luster material applied over the entire surface of the screen except for those elemental screen areas reserved for blue phosphor deposits and green phosphor deposits. While an improved screen structure for a tri-color picture tube was achieved by Kaplan, the inherent shortcomings of the optical filter art was still a factor to be contended with.
It is therefore a principal object of the invention to provide a novel screen structure for enhancing the contrast of an image produced by a cathode ray tube display device.
It is also an object of the invention to provide a cathode ray tube screen structure that exhibits attractive brightness, as well as reflectance, properties.
It is anothe object of the invention to provide an improved screen structure amenable to economical manufacturing processes.